Method of manufacturing ammonium nitrate



June 23, 1931. R. N. BoYD 1,811,712

METHOD oF MANUFACTURING AMMONIUM NITRATE Filed Dec. 14, 1927 ConneC/ed 70 ojoarce @famme/wa, /lyfacr :EA l 15 www/1f. 503% y Af Maf/www1 Patented June 23, 1931 UNITED STATES RICHARD N. BOYILOF ALLENTOWN, PENNSYLVANIA, ASSIGNORTO TROJAN tIOWXZDEIB,

COMPANY, F NEW YORK, N. IY.,

A `CORP013ATION OF NEW KVYORK METHODlOlEp'I/IANUEAGTURNG AMMONIUM NITRATE r yApplication iled ADecember 14, 19727. Seria1.No.1240,01-2.

The :principal objectof this `invention .is to provide novel Vmeans for `utilizing Weak "mixturesof nitriciacid Vapor and Water vapor containing up to .say 15% vof lnitric acid yby Weight in the manufacture of ammoniumV nitrate. l f

eak acid Vuaporsfof the ,above ltype are sometimes met With in vprocesses #for recoverf-ing nitric acid-trom `Waste or .spentacid `mixuo tures of nitric acid and .sulfuric acid. :These -vafpors may :beso #dilute as to render their recovery -as yWealnni'tric acid by. condensation 'or ,fas YWea-k lammoniu,m nitrate solution :unt economical, -anditis an 'object of the present '3135 invention, therefore, #to Aprovide veconomical means for' thefrecovery ofthesewveak-acids.

.I :havefdiscovered that :economical recovery of the :aoresaidweak :nitric acid in the xterm of ammonium nitrate may be accomplished ."210 fbfy rneut-nalizing the vWeak :mixtures of nitric acid vapor and Water vapor with ammonia, yeither i as ,a 'liquor -or las :ammonia bgas, 1n the Vpresence of :a hot-strong solution of .ammo- `n'ium nitrate. this process,.the sensible. i225 heat in the :hotWeak nitricacid vapors vand the heat liberatedby the reaction of ammonia Vand :ni-tric acid are suicientfto preventthe fwater `Napor, :entering with n1-tric g acid, 4from condensing, and @also Wherethe ammonia is 4i3@ introduced as :aqua ammonia, :to )evaporate vsome of fthe gwate-r 1thus y-brought `into thesystem so that practically all the -Water vapor entering-the systemvwiththe Initric yacid Vapor is kept vin LtheDVapor'fphase and -is exited -a-s '35 such( VWherefthe-ammonia isaddeda'saffgas,

fthe fheatl of reaction will serve to concentrate x,the .'anmlonium rnitrate solution circulating through :the system. 1 l

V4'-llhe operationoithe process Wifllberead-ibT 540 lunderstood Tfrom the following-Vdescription and :with reierence '.-to the attached '.draWin-g, which illustrates more orf-less `diaggammati vcally apparatusfmade in'accordance With the requirements :of the :present invention.v In

"45 ,'thefd'rawing, g1 designates a stripping column of standard :design includinga heating coil 2 which may be supplied with flive steam lfrom a suitable source. Agmgmoni-a'liquor Vis-introduced into the stripping column through an f5.0 niet pipe. 3 `4and the-residual liquor after thas'beenftreed from ammonia is Withdrawn fromfthe outlet .4. Theftop of the stripping column is `connected by a pipe 5 with an .absorbing column 6, and Athrough this pipe gas fromitjhe -ltopfof fthe'stripping column is ,e f

lconducted Vto :the rbottom of gthe absorbing column. Also 4connected to ,the vbottom sthelatter-column is a pipe 17 :through which fis admitted to the column fthe :mixture :of :nitric .acidandwvlaterfv-apor, low :in nitric acid. HotV ammonium :nitrate V solution i of say 40% tto strength `fis conducted tothe top -ot r-thetower --through la ;pipe"8, this pipe-ex- The invention may rbe practiced Without A.the stripping-tower Eby adding ,ammonia ttor .the absorber "6 as ammonia liquor. In kthis qeuent, the vsaidjlimior may be introduced (into 4--the absorber through :a pipe ;15 entering :the :absorber somewhat below the top thereof --as 'illustrated'. Pneierably x't-he entire ylequip- .ment :should rbe carefully insulated to conserve heat. e Y Y v p By the foregoing 'process fit-.hasfbeen found possible to produce a `concentrated solution yof ammonium ,nitrate Afrom .very dilute mixtures yof initric -a-cid `vaporrfvand Water vapor `and in 'theyabsence yet any v,considerable quantities ofxairiorother inert gases Without apgpl'ication of heat other .lthanythat already Vpresent in gtheventering vaporsand ,the heat of reaction of the ammonia Vwith the nitric acid. It "is not the intention, however, 1to -limi-t the ,process :to the'use `o wapors'without gadmixture with 4air or other inert gases, since the process will 4function when the Ymixed vapors contain considerable quantities yof mixed gases. The vapors and gases, however, must enter the absorber at temperatures near or above the boiling point of the mixture of the nitric acid and water vapor.

As a specific example of the operation of this apparatus for the recovery as ammonium nitrate of a mixture of nitric acid vapor and water vapor in which the nitric acid is of low concentration, I may introduce continuously the hot 15% HN0385% water vapor miX- ture from which it is desired to recover the nitric acid, into the bottom of the absorbing column G. The required ammonia for neutralizing the nitric acid as this nitric acid is supplied, is furnished continuously from the stripping column 1, the stripping column being fed with ammonia liquor ofany convenient NH3 content, as for example 25%, and the purpose of this stripping column being to separate the ammonia as NH3 gas containing a very small amount of water vapor from the ammonia liquor, leaving the water in which the ammonia was dissolved to form ammonia liquor to exit as a liquid from the trapped outlet 4;. The required heat for this stripping is supplied in the form of steam to the coil 2 with which the stripping column is equipped. Stripping columns are standard equipment and the details of their operation need not be described here.

The ammonia gas delivered from the stripping column is introduced into the bottom of the absorbing column 6 by means of the pipe 5. It is in the absorbing tower, which is a tall hollow column filled with a porous packing which permits comparatively free passage of gases and liquids, that the ammonia gas reacts with the nitric acid in the presence of a hot ammonium nitrate solution. The ammonia gas has already been explained as being introduced into the absorbing column by means of pipe 5 and the mixed nitric acid and water vapors from which the nitric acid is to be recovered'in the form of ammonium nitrate are introduced into the bottom of the absorbing column through the pipe 7. The ammonia, nitric acid vapor and water vapor mix and pass upward through the tower down through which is passed a boiling hot solution of ammonium nitrate which serves to collect and carry away the ammonium nitrate formed by the interreaction of the ammonia and nitric acid vapor. The water vapor with which the nitric acid vapor was present when introduced into the system passes on up through the column and exits to the air through the top of the column as a vapor. The boiling 60% solution of ammonium nitrate after passing down the absorbing column and collecting the ammonium nitrate formed by the reaction of the nitric acid vapor and the NH3 vapor iiows from the tower through pipe 1l to the storage tank 10 from which it is withdrawn continuously to pump 9 by means of which it is delivered into the top of the tower through pipe 8 in order to maintain a continuous circulation of hot ammonium nitrate solution down the absorption tower 6. The concentration of the ammonium nitrate s0- lution which is circulated through the absorber increases more or less while passing through the absorber due to its taking on the ammonium nitrate which was formed from the ammonia and the nitric acid vapor and is due possibly to a slight evaporation that may take place as a result of the generation of heat supplied by the reaction of the ammonia with the nitric acid. The strength of the ammonium nitrate solution can be adjusted for this increased concentration by adding water or weak ammonium nitrate solution either in tank l0 or to the stream of ammonium nitrate solution as it is fed into the top of the absorption tower. It is not essential to the process that the strength of the ammonium nitrate solution be kept at a uniform concentration so that wide variations in the strength of the ammonium nitrate solution Vare possible.

It will be seen that the quantity of ammonium nitrate solution in circulation is gradually increased and the make is withdrawn continuously or intermittently from tank 10 to the batch tank 13 where it is nally adjusted for neutrality whereupon it is available for the production of ammonium nitrate crystals by concentration and graining or crystallization. i

The novel feature of this invention is that the separation of the nitric acid vapor from the large quantity of water vapor with which it existed as a result of some preceding operation, is accomplished by permitting the ammonia gas and the ammonium nitrate so lution to selectively withdraw the nitric acid vapor from the vapor mixture passing up through the tower and permitting the water vapor to continue on as a vapor because there is no abstraction of heat which would be necessary before the vapor is changed to a liquid condition.

It is not intended that the apparatus used to carry out the absorbing step of the process be limited to an absorption tower because any other convenient methods of contacting the hot ammonium nitrate solution with the nitric acid vapor and the ammonia gas can be used. Neither is it the intention of placing a limitation as to the form in which the ammonia is supplied to the absorbing step, because the process is adaptable to the addition ofthe ammonia to the absorbing system in thc form of ammonia liquor. In case the ammonia is added in the form of ammonia liquor its addition should be made in such a way as to allow for ample contact between the nitric acid vapor and the ammonia.

I claim:

The method of concentrating an aqueous solution of ammonium nitrate, which coInacid. Y

RICHARD N. BOYD. 

